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Photodissociation is a critical process in the formation of photochemical smog. It involves the breakdown of molecules into smaller particles such as atoms or radicals through the absorption of light energy. In the given example, nitrogen dioxide (\(\mathrm{NO}_2\)) undergoes photodissociation when it absorbs a photon with sufficient energy. This results in the formation of nitric oxide (\(\mathrm{NO}\)) and an oxygen atom (\(\mathrm{O}\)).
The light required for photodissociation to occur must possess enough energy to break the molecular bonds. When light hits the molecule, the photon's energy breaks the chemical bond, creating new products. In the context of photochemical smog, photodissociation of nitrogen dioxide leads to the formation of reactive oxygen species, contributing to air pollution.

The electromagnetic spectrum is a range of all types of electromagnetic radiation, which includes visible light, radio waves, gamma rays, and more. Light with a wavelength of \(420\ \mathrm{nm}\) falls within the visible light portion of the spectrum, specifically towards the violet end. Visible light ranges from about \(380\ \mathrm{nm}\) (violet) to \(750\ \mathrm{nm}\) (red).

• Wavelengths towards the violet end of the spectrum possess higher energy compared to those closer to the red end.
• In the context of the given reaction, the \(420\ \mathrm{nm}\) wavelength of light provides just enough energy to break certain chemical bonds in \(\mathrm{NO}_2\)

Understanding where light falls on the electromagnetic spectrum helps predict its energy and what kind of chemical reactions it might drive.

Calculating bond energy is essential to understand the energy required to break a chemical bond. The bond energy calculation involves using the wavelength of light to determine the energy associated with a photon. Using the formula \(E = \frac{hc}{\lambda}\) where \(h\) is Planck's constant (\(6.626 \times 10^{-34}\ \mathrm{Js}\)) and \(c\) is the speed of light (\(3.00 \times 10^8\ \mathrm{m/s}\)), we can find the energy at given wavelengths.
For \(420\ \mathrm{nm}\) light, the energy is calculated as follows:
Convert \(\lambda\) to meters: \(420 \times 10^{-9} \ \mathrm{m}\)
Energy \(E = \frac{(6.626 \times 10^{-34}\ \mathrm{Js})(3.00 \times 10^8\ \mathrm{m/s})}{420 \times 10^{-9}\ \mathrm{m}} \approx 4.742 \times 10^{-19}\ \mathrm{J}\)
Converting to \(\mathrm{kJ/mol}\)
Using Avogadro's number \(6.022 \times 10^{23} \ \mathrm{mol}^{-1}\), the energy becomes \(285.33 \ \mathrm{kJ/mol}\).
This value indicates the maximum bond strength that a photon of \(420\ \mathrm{nm}\) light can break.

Lewis structures are diagrams that represent the valence electrons of atoms within a molecule. They provide insight into the molecular structure and the bonds between atoms.
In the photodissociation of nitrogen dioxide (\(\mathrm{NO}_2\)), Lewis-dot structures illustrate the breaking and formation of bonds.

• The initial Lewis structure of \(\mathrm{NO}_2\) depicts a double bond between nitrogen and one oxygen atom, and a single bond with the second oxygen, with unpaired electrons.
• After photodissociation, nitric oxide (\(\mathrm{NO}\)) forms, along with a single oxygen atom (\(\mathrm{O}\)) each retaining unpaired electrons.

These structures help visualize how molecules undergo changes during chemical reactions, such as photodissociation, displaying the distribution of electrons and the subsequent formation of new compounds.